THE EGG CAPSULES AND EMBRYOS OF THE PATAGONIAN GASTROPOD TROPHON PLICATUS (LIGHTFOOT, 1786) (CAENOGASTROPODA: TROPHONINAE) WITH REMARKS ON THE TAXONOMY OF THE SOUTHWESTERN ATLANTIC TROPHONINAE

摘要

Two species of Trophon are the most common muricids in Patagonian Atlantic waters, i.e. T. geversianus (Pallas, 1774)—type species of the type genus of the subfamily Trophoninae—and T. plicatus (Lightfoot, 1786). Trophon geversianus lives on intertidal and subtidal banks of mytilids (mainly Brachidontes spp.) along the Argentine coast. It ranges from the southern coast of Buenos Aires province to Burdwood Bank in the southwestern Atlantic, and up the Pacific coast of southern Chile. It is a characteristic element of the Magellanic biogeographic province. The egg capsules are frequent and very visible because of their distinctive erect pedunculate shape and bright yellow colour. Previous authors have described and illustrated in detail the shape and size of the eggs, egg capsules and embryos of this species (Zaixso, 1973; Penchaszadeh, 1976; D'Asaro, 1991; Cumplido et al., 2011). On the contrary, information about these structures in T. plicatus is very scanty. Pastorino (2005) revised the genus Trophon in South America and illustrated the variation of the adult shell, protoconch, operculum and radula of the latter species. However, no information on the capsules was available at that time. One probable reason is that this is a subtidal species only exposed during spring tides in some areas along the coast of southern Patagonia.